The present invention pertains to the field of computer systems. More particularly, this invention pertains to the field of integrated circuits with staggered bond pads.
FIG. 1 shows a cross-sectional view of a portion of a typical ball grid array semiconductor device 100. Among the components of the typical ball grid array semiconductor device 100 is a die 110. The die 110 is coupled to a lead frame 120 via a bond wire 115. Although only a single bond wire is shown in FIG. 1, a typical semiconductor device may include dozens or hundreds of such bond wires. The lead frame 120 provides electrical pathways from the bond wires to the solder balls 140. Although this example shows only three solder balls, a typical ball grid array semiconductor device may include dozens or hundreds of such solder balls. A solder mask 150 provides electrical isolation between the various solder balls 140. The entire assembly is encapsulated in a plastic casing 130.
FIG. 2 is a block diagram of a portion of a prior integrated circuit die with staggered bond pads. The staggered bond pads are represented by blocks 210 through 217. The bond pads are arrayed in close proximity to the edge of the die (indicated by line 260). Although only eight bond pads are depicted in FIG. 2, a typical prior integrated circuit with staggered bond pads may include hundreds of such bond pads. The bond pads 210 through 217 when assembled into a complete semiconductor device would be connected to a lead frame via bond wires, as seen in the example of FIG. 1.
The bond pads 210 through 217 are electrically coupled to a series of driver/ESD circuit cells 220 through 227. The term xe2x80x9cESDxe2x80x9d refers to xe2x80x9celectrostatic dischargexe2x80x9d. The driver/ESD cells 220 through 227 provide drive strength for output signals, receive input signals, and also provide ESD protection. The driver/ESD cells 220 through 227 are coupled to the bond pads 210 through 217 via metal connections. Two of the metal connections are labeled 240 and 247. Metal connection 240 connects bond pad 210 to driver/ESD cell 220, and metal connection 247 connects bond pad 217 to driver/ESD cell 227. The driver/ESD cells 220 through 227 are connected to a series of pre-driver cells 230 through 237. These cells serve to couple the driver/ESD cells with the circuitry located at the die core.
Because the bond pads 210 through 217 are arranged in a staggered array, with an inner ring including bond pads 211, 213, 215, and 217 and with an outer ring including bond pads 210, 212, 214, and 216, the metal connections to the outer ring bond pads must be routed between the inner ring bond pads.
It is often advantageous for a semiconductor device manufacturer to reduce the size of a die in an effort to produce more devices per wafer, thus reducing manufacturing costs per device. If the number of bond pads on the die is not to decrease, then the bond pads must be placed in closer proximity one to another when the size of the die is reduced. This, in turn, results in a more narrow metal connection between the driver/ESD cells and the bond pads in the outer ring. Also, the width of the driver/ESD cells is reduced.
Several problems can arise as the width of the metal connections between the driver/ESD cells and the bond pads in the outer ring is reduced. A more narrow metal connection results in greater electrical resistance. The narrow connection may not be able to handle large currents that may occur as a result of an ESD event. The narrow metal connection may also experience electro-migration, which is a gradual erosion of the metal resulting in eventual circuit failure. One potential solution to the narrow metal connection problem may be to route additional metal on layers below the inner row of bond pads, but this potential solution raises a manufacturing problem of dielectric material that is typically deposited between metal layers cracking below the bond pads during installation of the bond wires.
In addition to the problems raised due to a reduction in width of the metal connections between the driver/ESD cells and the bond pads in the outer ring, a reduction in the width of the driver/ESD cells may make implementation of ESD protection structures within the driver/ESD cells more problematic.